Trench isolation is a commonly employed scheme for achieving sidewall isolation in a variety of semiconductor architectures, such as silicon on insulator (SOI), including separation by implanted oxygen (SIMOX) and bonded wafer technologies, as well as PN junction isolation structures. Within the semiconductor wafer (e.g. silicon substrate), the trench is coated with an insulator material (typically oxide) and then filled with a material such as polysilicon, which is often electrically floating. Although a bias voltage may sometimes be applied to the poly-fill material in order to control parasitic sidewall MOS devices (for which the polysilicon fill acts as a gate), the essential function of the trench is to provide isolation among the islands of the substrate. Interconnect among circuit device regions has typically been accomplished by in situ diffusions within the islands and conductor tracks overlying a topside insulator layer.
In my U.S. Pat. No. 5,057,895, entitled: "Trench Conductor and Crossunder Architecture," issued Oct. 15, 1991, and my U.S. Pat. No. 5,196,373, entitled: "Method of Making Trench Conductor and Crossunder Architecture," issued Mar. 23, 1993, the disclosure of each of which is herein incorporated, I have described a new and improved dielectrically isolated trench semiconductor architecture and method of making that architecture, in which trench material (conductively doped polysilicon fill) is used as an interconnect structure for circuit devices that are supported within dielectrically isolated islands of a semiconductor substrate, thereby decreasing the amount of topside interconnect and thus reducing the potential for parasitics beneath tracks of surface metal.
Such a trench architecture may be employed to distribute one or more voltages to dielectrically-isolated islands of the substrate, by using a dielectric-coated trench grid pattern to subdivide the substrate into a plurality (e.g. matrix) of spaced-apart dielectrically isolated islands. Conductive material (e.g. doped polysilicon or polysilicon with a layer of resistivity-decreasing refractory material, such as a layer of tungsten) is formed in the dielectric-coated trench grid pattern and coupled to receive a prescribed voltage to be distributed throughout the substrate. Respective contact regions of islands that are to be electrically connected to a reference voltage are connected via local interconnects bridging oxide vias overlying the contact regions and adjacent locations in the trench grid pattern.
In addition to providing voltage distribution capability, the conductive fill material of a trench may be used to provide crossunders, i.e. interconnects that pass beneath and are electrically isolated from a surface conductor track, between regions of the same island or regions of separate islands. Respective contact regions of the island or islands are electrically interconnected to the conductive material in the trench via local interconnects bridging oxide vias overlying the contact regions and the adjacent locations in the trench.
The cross-under function may also be effected by providing one or more auxiliary dielectric-coated trench regions in at least one of the islands, such that a surface conductor overlies the surface of the one or more auxiliary trench regions in the one island between spaced apart locations of the island, the crossunder extending between the spaced apart island locations. Respective conductive layers provide electrical connections to these spaced-apart locations of the auxiliary trench regions and other portions of the circuit.